The present disclosure relates generally to chemically amplified photoresists for use in the manufacture of integrated circuit devices, and more particularly, to a method for increasing resolution of a patterned chemically amplified photoresist.
In the manufacture of semiconductor integrated circuits, many well known photolithography techniques are used to pattern the various functional features on different levels of an integrated circuit chip. Generally, photolithography involves selectively exposing regions of a photoresist coated silicon wafer to a light radiation pattern, and then developing the exposed photoresist in order to selectively protect regions of wafer layers, such as metallization layers, oxide dielectric layers, polysilicon layers, silicon layers, and the like, from subsequent etching operations.
As is well known, a photoresist is a light radiation-sensitive material that is typically spin-coated over a selected layer of a silicon wafer. The photoresist material is classified as either positive or negative depending on how it chemically reacts to light radiation during exposure. Positive photoresist, when exposed to radiation becomes more soluble and is thus more easily removed during the development process. In contrast, negative photoresist will generally become less soluble when exposed to radiation, thereby enabling the removal of non-exposed regions.
A chemically amplified photoresist is a photoresist to which an acid catalyst reaction is applied. The chemically amplified photoresist generally comprises a base resin having acid labile pendant groups, a photoacid generator, small amounts of additives for performance adjustment, and an organic solvent for spin coating the photoresist onto a substrate. Chemically amplified photoresist compositions may rely on deprotection reactions per unit of photogenerated acid to effect a change in dissolution properties between exposed and unexposed regions. In the deprotection mechanism, upon exposure to activating radiation, a catalytic amount of hydrogen ions (acid) is generated by the photoacid generator, which catalytically cleaves the pendant acid labile groups from the base resin to form polar groups and render the irradiated photoresist soluble to alkali. Those areas of the photoresist that were not exposed to activating radiation are generally not soluble in alkali, thereby providing a dissolution differential between exposed and unexposed regions during development. Following development, the surface of the semiconductor substrate can be selectively etched by using the photoresist pattern described above as a mask.
Although chemically amplified photoresists work relatively well, as smaller and smaller feature sizes are designed for higher performance integrated circuit devices, the resolution of these high performance designs have been exemplifying less than acceptable resolution due to poor photoresist development. Moreover, resolution is limited by the wavelength of exposure.